1. Field of the Invention
The present invention relates to a device and method used in conjunction with high pressure presses in the areas of isostatic pressing and the high pressure treatment of  substances. The present invention relates to a type of wear liner for use in high pressure presses and a method for fitting and replacing the wear liner.
2. Description of the Related Art
For some time now high pressure treatment has been used as a method for inactivating micro-organisms and certain enzymes in foodstuffs and other provisions. A decisive factor for obtaining a good result from a high pressure treatment is that the pressure is sufficiently high. During treatment of provisions, the pressure is usually set at a pressure between 1,000–15,000 bar. Inside high-pressure presses, the high working pressure is generated inside the innermost cylinder, or inner liner, that defines the pressure chamber. At such high pressures, the inner liner is subjected to very great fatigue stress. Liner failure unavoidably arises after some time in operation and so the inner liner is usually designed and made as a wear liner, which is replaceable. To avoid liner failure, the wear liner is regularly replaced well in advance of the estimated service life. Such liners are expensive and consequently economically disadvantageous. Further, each wear liner replacement constitutes a time consuming and costly process. PCT/SE95/000153 describes a particular type of wear liner, which is installed in a high pressure press of the pre-stressed wire-wound type.
Wear liners have to be replaced due to wear or fracture. The replacement operation includes a removal stage in which the wear liner is removed and an insertion stage in which a new wear liner is put in place. To remove a worn wear liner with, for example, a wire-wound press of the type described in PCT/SE95/000153, the piston part of the inner pressure intensifier of the press is arranged with specially adapted tools so that pressure can be brought to bear on the liner holder and the wear liner. Pressure from the inner pressure intensifier is applied to the liner holder and the wear liner and they are driven out of the cylindrical pressure chamber together under pressure. A new wear liner is placed in position inside a liner holder and driven into place inside the cylindrical pressure chamber of the press by the internal pressure intensifier, which is combined with special tools. In the wire-wound press described in PCT/SE95/000153 both the interior of the cylindrical pressure chamber and the exterior of the liner holder are slightly conical in their cylindrical shape, shown schematically as prior art in FIG. 1. The interior of the liner holder is cylindrical in shape. The wear liner is  placed in the liner holder as a shrink fit. When the liner holder with the wear liner placed inside it is driven into the cylindrical pressure chamber of the press they become compressed and thereby pre-stressed in the radial direction in order to withstand high pressures under use.
As stated above, liner failure can arise after some time in operation. A feature of the wear liner described in PCT/SE95/000153 is that it is a very thin walled cylinder. This is designed such that in the event of a liner fracture, the additional force that might overload the press frame, which force is proportional to the cross section of the wear liner, is small. This means that the additional force due to the fracture can be safely confined within the press avoiding expensive or dangerous damage to the press or its surroundings.
A further feature of the wear liner described in PCT/SE95/000153 is that it has a means on the outside of the wear liner, for example a spiral groove cut along the whole length of the outside surface of the wear liner. Thus, if a wear liner should crack or split in service, then pressurized medium from the high pressure chamber leaks out of the wear liner. The pressurized medium that has leaked is conducted to the outside of the press via a groove or other means in the outer envelope surface of the wear liner. This indicates that a crack or split in the wear liner has occurred and that appropriate action must be taken and the wear liner replaced.
A disadvantage with the wear liner described in PCT/SE95/000153 is that it has to be mounted inside a wear liner holder, a cylinder with a conical exterior, which is expensive to manufacture. Its use is limited to presses with an internal pressure intensifier or a piston similarly capable of driving the wear liner in and out of the press. It is a lengthy and difficult process to remove the wear liner, as the wear liner and the liner holder have to be driven out of the press by the internal pressure intensifier combined together with special tools. The wear liner with the liner holder is also lengthy and difficult to install, as it has to be carefully driven into the press using the internal pressure intensifier together with special tools in order to position the conical liner holder, with the wear liner inside it, inside the cylindrical pressure chamber in a pre-stressed condition.
In addition to the wire-wound pre-stressed press of the type described in PCT/SE95/000153 there are alternate designs for high pressure presses. High pressure presses may or may not have cylindrical pressure chambers that are pre-stressed. For example, a sufficiently thick steel cylinder may be used as the cylindrical pressure chamber of a high  pressure press without pre-stressing. However, this type of press requires frequent safety inspections for signs of damage when operated at higher pressures. Damage to such thick, heavy cylindrical pressure chambers entails expensive repairs or replacements.